计算一接地金属槽，其上盖对地绝缘且具有电位 ，侧壁与底壁为地电位。用有限差分法编程计算凹槽内的电位分布。-Calculation of a metal tray earthing, the upper cover on the insulation and has potential, side wall and the bottom wall to ground potential. Calculation of potential distribution in the groove with the finite difference method programming.